Process control systems, such as distributed or scalable process control systems commonly found in chemical, petroleum or other industrial processes, typically include one or more process controllers communicatively coupled to one or more field devices via analog, digital, or combined analog/digital buses. The field devices may include, for example, control valves (e.g., pressure regulators) valve positioners, switches, and transmitters (e.g., temperature, pressure and flow rate sensors). The field devices perform functions within the process such as opening or closing valves, measuring process parameters, and performing basic diagnostics. The process controller receives signals indicative of process measurements made by the field devices, or may receive other information pertaining to the operation or status of the field devices. The process controller then uses this information to execute or implement one or more control routines to generate control signals, which are sent over the buses to the field devices to control the operation of the process. Information from each of the field devices and the controller is typically made available to one or more applications executed by one or more other hardware devices, such as host or user workstations, personal computers or computing devices. In turn, such applications enable an operator to perform any desired function regarding the process, such as setting parameters for the process, viewing the current state of the process, modifying the operation of the process, or other desired functions.
Conventionally, control valves and pressure regulators include a pneumatic actuator. These actuators typically include a diaphragm disposed within a spring case or casing, and the casing includes a vent hole that facilitates the movement of air into and out of the casing as the diaphragm of the control valve moves in response to pressure changes in the process fluid. The vent hole thus serves to maintain the pressure on one side of the diaphragm at atmospheric pressure.
Moreover, when the control valve is installed in an internal environment (e.g., in a process control room), vent piping is fluidly coupled to the vent hole. The vent piping runs to an ambient or external environment, such as outside or another safe location. In the event that a diaphragm or some other component of the control valve fails, the vent piping can vent process gas from within the control valve to the external environment, such that the process gas is not vented into or within the internal environment and/or does not damage the control valve. However, installing and maintaining vent piping can be costly and require significant amounts of time, and vent piping, once installed, can take up significant amounts of space.